Analysis of Genetic Variation in Dog Breeds
About Humans have created various dog breeds in an effort to select for desirable phenotypic traits such as shape, size, coat color, and demeanor. As a result of this selective breeding, it is likely an alteration in the present genetic information among various breeds has taken place. To further investigate the genetic variation between breeds, a study was preformed which looked at the genomes of 28 different dog breeds, seven of which were recognized breeds of the American Kennel Club. Dog breeds are considered intraspecies groups containing relatively uniform physical characteristics, developed under controlled conditions by humans. As of recently, dog breeds have been developed from existing breeds where each foundation breed provided a phenotypic trait that proved to breed true in offspring. Based on current breeding histories, most popular dog breeds recognized today are a result of breeds developed in the 19th century. Rapid phenotypic selection has lead to the most vast range of diversity than any other animal species. Strong inherent selection pressure seen in the development of domestic dog breeds can show a loss of genetic diversity in some breeds, while others may exhibit new traits as a result of breeding histories and practices. Materials and Methods Once the appropriate dogs and breeds were selected for the study, a sample PCR was preformed in an effort to amplify canine genomic DNA. All samples used in the study were derived from buccal cells obtained by bristle cytology brushes. After the PCR reaction was run, gel electrophoresis was used for DNA fragment analysis. The DNA fragment analysis was preformed using STRand software, and then a statistical analysis was done. Marker polymorphisms were determined by the relative number and frequency of alleles for a certain locus within each breed. Allele number and frequencies were determined by counting, and a phylogenetic tree was constructed using allele frequencies from a subset of 66 genetic markers used to compute a matrix of genetic distances. Analysis of genotypes After genomic analysis, it was found that the amount of genetic variation was considerable, with a total heterozygosity of 0.618 with a range of 0.327 to 0.758. Significant differences were found between the least and most heterozygous breeds within the seven groups, with the terrier bread showing the most divergence. Dog breed size was estimated by averaging the size of the dogs registered to the American Kennel club for 5 consecutive years. A 100-fold difference between the smallest and largest dog breed was estimated. In order to determine the effect on the wide range of heterozigosity, the heterozigosity vales were plotted against estimated population size. There was only a slight correlation found between the population size and heterozigosity (3%), however a stronger correlation was determined between the date of breed recognition and heterozigosity. More recently recognized breeds showed a 19% higher heterozygosity than in earlier recognized breeds showing more genetic variation in newer breeds. Researchers were also interesting in determining if the number of alleles per breed changed relative to the total number of alleles, and to what extent this was influenced by population size and time since registration. The total number of alleles for all breeds was 1780, with a range of 399 to 805 alleles within each breed. In terms of population size, the breeds with the smaller populations contained fewer alleles than larger populations. Altogether, the heterozigosity and Hardy-Weinberg equilibrium decreased as the population size decreased, and as the length of time in the registry increased. The miniature bull terrier on the other hand did not follow this trend. This specific breed had 22.5% heterozigosity than the bull terrier. The miniature bull terrier originated from the terrier and has a population size that is 1/10 that of the bull terrier. Due to this anomaly, it is thought that either the miniature bull terrier experienced an outcorssing, or the bull terrier underwent a genetic bottle neck, causing the two breeds to diverge. References 1. [http://jhered.oxfordjournals.org/content/94/1/81.long#T1 Irion, D.N. "Journal of Heredity." Analysis of Genetic Variation in 28 Dog Breed Populations With 100 Microsatellite Markers. Journal of Heredity, n.d. Web. 24 Nov. 2014.] 2. [[wikipedia:Hardy–Weinberg_principle|"Hardy–Weinberg Principle." Wikipedia. Wikimedia Foundation, 17 Nov. 2014. Web. 24 Nov. 2014.]]